Various types of magnetoresistive random access memory (MRAM) store data using magnetic tunnel junctions. A magnetic tunnel junction (MTJ) may include “fixed” and “free” magnetic layers, where a magnetic moment of the free layer may be switched to be parallel or antiparallel to a magnetic moment of the fixed layer. A thin dielectric or barrier layer may separate the fixed and free layers, and current may flow across the barrier layer due to quantum tunneling. A difference in resistance between parallel and antiparallel states allows data to be stored. For example, a low resistance may correspond to a binary “1” and a high resistance may correspond to a binary “0,” Alternatively, a low resistance may correspond to a binary “0” and a high resistance may correspond to a binary “1.
As storage capacities increase and MTJ feature sizes decrease, decreasing the volume of an MTJ may decrease the thermal stability of the free layer's magnetic moment. Decreased thermal stability may result in poor data retention and increased error rates. However, increasing the thermal stability of an MTJ's free layer in other ways to compensate for the decreased volume may also increase the write voltage used to set the free layer into the parallel or anti-parallel state. In various types of MTJs, configuring a free layer so that it is not easily switched into a different state by thermal energy fluctuations may also involve increasing the energy it takes to deliberately switch between states.